The invention relates generally to optical data storage media, and more specifically, to holographic storage media.
Optical storage media generally provide an effective platform for archiving data, offering numerous advantages over other forms of data storage in terms of cost of the medium, life expectancy of the stored data, the amount of time required to write data, and the amount of time required to access the data. Holographic storage is a specific type of optical storage in which data is written to and read from the optical medium as holograms. These holograms are images formed by the interaction of multiple beams of light in a photosensitive layer within the volume of a holographic medium. That is, for example, using a combination of a reference light beam and a signal light beam, a three-dimensional interference pattern may be formed in the holographic medium as certain species present are chemically modified by the beams, modulating the refractive index of specific portions of the holographic medium.
In such a holographic medium, a reverse saturable absorber (RSA) may be used as an energy-transfer threshold dye. In general, an energy-transfer threshold dye may be generally responsible for absorbing recording light (e.g., from the reference beam and signal beam) and causing a chemical reaction to occur. That is, when the recording light is beyond a particular intensity threshold, the RSA dye may be absorb multiple photons of recording light and then transfer the energy of the excited state to a reactant species (e.g., an index change material). In response, the reactant species may undergo a chemical reaction (e.g., dimerization reactions, isomerization reactions, or inter- or intra-molecular condensation reactions), which may cause a localized change in the refractive index of the holographic medium, essentially capturing the intensity and phase of the recording light. Subsequently, upon interrogating the holograms using a lower intensity of light, this captured information may be recovered in a nondestructive fashion such that the associated encoded data may be deciphered. However, the RSA dye should have sufficient sensitivity to enable efficient recording of data to the holographic medium.